Electromagnetic clutches are used to drive a variety of mechanical devices including vehicle air conditioning compressors. These clutches are engaged and disengaged as required to drive the compressor when cooling is required and to inactivate the compressor when cooling is not required. To engage an electromagnetic clutch current is supplied to an electromagnetic coil. Current in the coil creates an electromagnetic force which draws an armature and rotor together. Torque is transferred from the rotor through the armature when the clutch is engaged. To disengage the electromagnetic clutch the coil is disconnected from a power source thereby eliminating the electromagnetic force that holds the armature and the rotor in contact with each other.
The electromagnetic clutch includes a rotor assembly, an armature assembly, and a field assembly. The rotor of the assembly is rotatively journaled on a tubular projection on a compressor housing that is concentric with the compressor drive input shaft and a central axis of the compressor. The rotor has an armature contact surface, a torque input member that can be driven by a belt, chain, gear or other torque transfer system, and a toroidal chamber for an electromagnetic coil in the field assembly. The armature is attached to an armature hub that is secured to a compressor drive input shaft. The armature is axially movable along the central axis of the compressor into and out of engagement with the armature contact surface on the rotor. The electromagnetic coil is part of a field assembly. The field assembly includes a ring and flange assembly. The ring portion of the ring and flange assembly has a toroidal chamber with a U-shaped cross-section. A flange is attached to the ring portion of the ring and flange assembly. The flange is attached to the compressor housing with the ring portion projecting into the toroidal chamber in the rotor assembly. An electromagnetic coil is enclosed in a bobbin and cover and pressed into the toroidal chamber in the ring and flange assembly and secured in place. Two lead wires extend from the electromagnetic coil through passages through the ring and flange assembly. The two wire leads that extend from the electromagnetic coil are connected to terminals. The terminals are connected to a power source to energize the electromagnetic coil and create a magnetic force that pulls the armature into contact with the armature contact surface on the rotor to engage the clutch. The terminals are disconnected from a power source to deenergize the electromagnetic coil, allow the armature to move out of contact with the armature contact surface and disengage the clutch.
A number of different terminal assemblies have been connected to the two wire leads that extend from the electromagnetic coil. These terminal assemblies and their connection to the two wire leads are critical. The wire leads from the electromagnetic coil are small and relatively easy to break. The wire leads from the electromagnetic coil are frequently broken when they are merely attached to larger leads with a terminal. Movement of the large lead and terminal bends the wire leads from the electromagnetic coil and eventually breaks the wire lead.
Terminals have been successfully attached to the electromagnetic coils by employing a terminal housing that is integral with the bobbin. A large port is required in the ring and flange assembly for the passage of the terminal housing. The terminal housing frequently extends out of the ring and flange assembly too far making it difficult to secure terminals and a terminal cover to the terminal housing. The terminal housing may also fail to extend out of the ring and flange assembly to a position which will permit the terminals and the terminal cover to be properly aligned with a terminal housing and secured to the ring and flange assembly. If the terminal housing does not pass out of the ring and flange assembly far enough, the terminals and terminal cover cannot be aligned with the terminal housing and attached to the ring and flange assembly properly. Occasionally the terminal cover is secured to the ring and flange assembly in a position which results in a bending load, a shear force or a twisting load being applied to the terminal housing that is integral with the bobbin. These loads can cause the bobbin and terminal housing to break. Improper positioning of the terminal cover and a loose terminal cover can lead to a failure of the connection between the terminals and the leads from the electromagnetic coil.